As is well known, as the circuit density of electronic chip devices increases, there is a correspondingly increasing demand for the removal of heat generated by these devices. The increased heat demand arises both because the circuit devices are packed more closely together and because the circuits themselves are operated at increasingly high clock frequencies. Nonetheless, it is also known that runaway thermal conditions and excessive heat generated by chips is a leading cause for failure of chip devices. Furthermore, it is anticipated that the demand for heat removal for these devices will increase indefinitely. Accordingly, it is seen that there is a large and significant need to provide useful cooling mechanisms for electronic circuit devices.
The use of thermoelectric cooling elements is known. These elements operate electronically to produce a cooling effect. By passing a direct current through the legs of a thermoelectric device, a temperature difference is produced across the device which is contrary to that which would be expected from Fourier's Law.
At one junction of the thermoelectric element both holes and electrons move away, toward the other junction, as a consequence of the current flow through the junction. Holes move through the p-type material and electrons through the n-type material. To compensate for this loss of charge carriers, additional electrons are raised from the valence band to the conduction band to create new pairs of electrons and holes. Since energy is required to do this, heat is absorbed at this junction. Conversely, as an electron drops into a hole at the other junction, its surplus energy is released in the form of heat. This transfer of thermal energy from the cold junction to the hot junction is known as the Peltier effect.
Use of the Peltier effect permits the surfaces attached to a heat source to be maintained at a temperature below that of a surface attached to a heat sink. What these thermoelectric modules provide is the ability to operate the cold side below the ambient temperature of the cooling medium (air or water) or provide greater heat removal capacity for a given cold plate or component temperature. When direct current is passed through these thermoelectric modules a temperature difference is produced with the result that one side is relatively cooler than the other side. These thermoelectric modules are therefore seen to possess a hot side and a cold side, and provide a mechanism for facilitating the transfer of thermal energy from the cold side of the thermoelectric module to the hot side of the module.